CN107367904B

CN107367904B - Photoetching light cover of extreme ultraviolet light

Info

Publication number: CN107367904B
Application number: CN201710285380.1A
Authority: CN
Inventors: Z·J·齐; C·A·特利; J·H·兰金
Original assignee: GlobalFoundries Inc
Current assignee: GlobalFoundries US Inc
Priority date: 2016-04-27
Filing date: 2017-04-27
Publication date: 2020-02-28
Anticipated expiration: 2037-04-27
Also published as: US9946152B2; DE102016209765B4; TW201738651A; US20170315438A1; TWI613507B; DE102016209765A1; CN107367904A

Abstract

The present disclosure relates to extreme ultraviolet lithography reticles, and more particularly to modified surfaces of extreme ultraviolet lithography reticles and methods of making the same. The structure includes a reflective surface having a patterned design, and a black border region at an edge of the patterned design. The black border region includes a modified surface morphology to direct light away from subsequent reflectors.

Description

Photoetching light cover of extreme ultraviolet light

Technical Field

The present disclosure relates to reticle structures, and more particularly, to modified surfaces of extreme ultraviolet lithography reticles and methods of making the same.

Background

Due to the significantly narrower illumination wavelength (λ ═ 13.5 nm), Extreme Ultraviolet (EUV) lithography is likely to complement and ultimately replace conventional Deep Ultraviolet (DUV) lithography, which may provide, among other benefits, enhanced patterning resolution and lower process complexity. EUV is currently being developed into immersion lithography (immersion lithography) that may incorporate 32 nm pitch resolution in the future, sometimes referred to as 7 nm node.

Optical components used in EUV lithography are based on reflective rather than refractive optics. EUV reflectors (mirrors) consist of alternating layers of material (e.g. molybdenum and silicon), also referred to as multilayers. EUV reticles utilize reflective coatings other than EUV absorbing material that has been etched (patterned) to reveal the desired circuit design. However, current absorbers for EUV lithography cannot absorb all EUV light, but actually have a reflectivity of about 1 to 3%, depending on the absorber height. EUV reticles also exhibit overlapping shot with adjacent fields, which can produce 1.5% to 5.0% on the edges of the circuit design and 4.5% to 15% additional background light on the corners. The Critical Dimension (CD) impact per percentage of the wafer may be above about 1 nanometer, resulting in a large reduction in the Critical Dimension (CD).

Disclosure of Invention

In one aspect of the present disclosure, a structure comprises: a reflective surface comprising a patterned design; and a black border region at an edge of the patterned design. The black border region includes a modified surface morphology to direct light away from subsequent reflectors.

In one aspect of the present disclosure, a structure comprises: a substrate; a back metal on a surface of the substrate; a reflective surface on an opposite surface of the substrate, the reflective surface comprising a plurality of alternating layers of relatively high and low atomic number materials; a protective coating on the reflective surface; an absorption layer on the protective coating; a patterned design formed within the absorber layer up to the protective coating; and a black border region formed through the reflective surface, the protective coating and the absorbing layer to expose a surface of the substrate. The black border region comprises a modified surface morphology of the substrate.

In one aspect of the present disclosure, a method comprises the steps of: forming a black border region in the mask; and modifying the surface morphology of the black border region to cause deep ultraviolet light to scatter away from reaching the next reflector.

Drawings

The present disclosure is described below in embodiments with non-limiting examples of exemplary embodiments of the disclosure referring to the several figures.

FIG. 1 illustrates a mask structure having a modified surface morphology in accordance with aspects of the present disclosure.

Fig. 2 a-2 c illustrate different surface morphologies within the black border region according to several aspects of the present disclosure.

Detailed Description

The present disclosure relates to reticle structures, and more particularly, to modified surfaces of extreme ultraviolet lithography reticles and methods of making the same. More particularly, the present disclosure relates to structures and methods for suppressing Deep Ultraviolet (DUV) radiation from affecting the imaging boundary of an Extreme Ultraviolet (EUV) reticle. Advantageously, the masks described herein may include a modified surface morphology in the "black border" (BB) region, such that reflected DUV light is scattered off preventing it from reaching the next reflector, thereby reducing or eliminating radiation that overlaps on circuit design elements. In this way, it is possible to maintain critical dimensions of the circuit design at the edges and corners of the exposure field.

EUV reticles are typically made as flat as possible to suppress focus drift and improve depth of focus. Furthermore, the overlay of EUV light with adjacent fields results in an over-development of Critical Dimensions (CD) by removing the absorbing material and multi-layer regions around the exposed fields to create "black border" regions. By modifying the mask including the black border region, the EUV reflectivity at the black border region may be reduced to less than about 0.05%. Furthermore, the reflectivity of the non-photoreactive region (150 nm > λ >300 nm) may be reduced to about 5 to 6%. In order to clean and reduce potential particle sources and to exploit etch selectivity, the surface morphology of the black border region is typically etched as flat and uniform as possible. However, the flat surface may still reflect DUV despite reducing EUV reflection from the black border region. The DUV reflectivity may be about 5% to 6%, which still affects wafer CD causing CD to drop from 0.5 nm to 0.6 nm at the edges and 1.5 nm to 2 nm at the corners of the circuit design exposure field. Furthermore, the target DUV reflectivity must be less than 1.5% to reduce the impact on wafer CD to an acceptable level.

A solution to the above problem is to reduce the DUV light reaching the next reflector in the scanner optics by adding an EUV transmissive structure (e.g., silicon) on the reflector surface to scatter the unwanted DUV radiation. However, this is very difficult to implement. Advantageously, the present disclosure provides an improved solution to the above-mentioned problems while avoiding the disadvantages of other solutions, such as complexity of implementation. In particular, the surface of the light shield described herein in the black border region is deliberately modified to allow the reflected DUV light to be scattered away and prevent it from reaching the next reflector.

The mask structure of the present disclosure can be made in a number of ways using different tools. Generally, however, the methods and tools are used to form structures with dimensions on the micrometer and nanometer scale. The methods, i.e., techniques, used to fabricate the mask structures of the present disclosure have been developed in the Integrated Circuit (IC) art. For example, the structures are built on a wafer and patterned on the wafer with a photolithographic process to achieve a thin film of material. In particular, the fabrication of the mask structure uses the following 3 basic building steps: (i) depositing a thin film of material on a substrate, (ii) laying down a patterned mask on top of the thin film using photolithographic imaging, and (iii) etching the thin film selectively to the mask.

FIG. 1 illustrates a mask structure having a modified surface morphology in accordance with aspects of the present disclosure. In particular, the mask structure 10 includes a backside material 12 formed on a substrate 14. In several embodiments, the backing material 12 may be a chrome or other metal coating. The chromium or other metal coating may be formed using conventional CMOS techniques such as electroplating or other deposition methods (e.g., PECVD for other metals) as are known to those skilled in the art. In several embodiments, the backside material 12 is placed on the chuck using electrostatic forces. The substrate 14 may be, for example, a glass substrate, although other non-reflective materials are contemplated herein.

Still referring to FIG. 1, a multilayer reflective coating 16 is formed on the substrate 14. As illustrated, for the back side material 12, a multilayer reflective coating 16 is formed on the opposite surface of the substrate 14. In several embodiments, the multilayer reflective coating 16 comprises alternating layers of high and low atomic number materials (atomic number materials). For example, alternating layers of high and low atomic number materials may comprise defect-free molybdenum/silicon multilayers for reflecting light by means of interlayer interference. As is well known to those skilled in the art, molybdenum has a high atomic number; however, silicon has a low atomic number. In several embodiments, other materials with low atomic numbers, e.g., Z in the 10 range, and other materials with high atomic numbers, e.g., Z in the 40 range, may be used. Furthermore, in several embodiments, the multilayer reflective coating 16 may be used as an etch stop layer (etch stop) and a protective layer for subsequent processes.

In several embodiments, more than 40 or more layers of material may be used to form the multilayer reflective coating 16. These layers may be deposited by conventional deposition methods, such as Chemical Vapor Deposition (CVD) processes. In several embodiments, the uppermost layer of the multilayer reflective coating 16 should be a high atomic number material, e.g., a material with a high reflectivity.

Fig. 1 further illustrates the protective coating 18 formed on the front surface of the multilayer reflective coating 16. In several embodiments, the protective coating 18 is a thin film that protects the multilayer reflective coating 16 from degradation under continued use of the reticle 10. In several embodiments, the protective coating 18 is a material having a high atomic number, e.g., Z in the range of 40. For example, the protective coating 18 can be ruthenium; however, other materials having high atomic numbers are also contemplated herein. The protective coating 18 can be formed on the multilayer reflective coating 16 to a thickness on the order of nanometers, for example, about 2 nanometers, using conventional deposition processes. In several embodiments, the protective coating 18 may be deposited by Ion Beam Deposition (IBD).

An absorbent material 20 is formed on the protective coating 18. In several embodiments, the absorber material 20 may be a tantalum-based material, such as tantalum nitride; however, other known absorbent materials are also contemplated for use in the structures described herein. The absorber material 20 may be deposited to a thickness of about 50 nanometers to about 70 nanometers; however other thicknesses are contemplated herein. Those skilled in the art will appreciate that although the thickness of absorbing material 20 may have a significant impact on 3D mask effects such as horizontal-vertical misalignment due to the mask, pattern shift through the focus, and loss of image contrast through the reflective mask coating due to side lobe reduction (apodization). In several embodiments, the absorber material 20 may be deposited by a conventional deposition method, such as a CVD process.

In several embodiments, the reticle 10 is subjected to photolithography and etching processes to form the pattern 22 and the black border region 24. It should be appreciated that pattern 22 represents a circuit design element; however, a black border region 24 is provided around the edges of the pattern to prevent radiation overlap, as described herein. That is, the black border region 24 reduces the DUV reflectivity, which affects the wafer CD causing CD degradation at the edges and corners of the circuit design.

As illustrated by a more specific embodiment, the pattern 22 can be formed by placing a resist on the absorbing material 20 and exposing it to energy (e.g., light) to form an opening (pattern). Absorber material 20 may then be patterned, e.g., etched to form openings, using conventional etching techniques and chemistries that are selective to absorber material 20. In several embodiments, the etching technique may comprise a dry etching process, such as a reactive ion etching process (RIE). In several embodiments, the protective coating 18 acts as an etch stop layer during the etching process. The resist may then be removed by conventional processes, such as oxygen ashing or other cleaning techniques known to those of ordinary skill in the art.

Similarly, the black border region 24 may be formed using conventional photolithography and etching processes. However, in this process, the black border region 24 will form up to the underlying substrate 14. In this way, the surface of the substrate 14 is exposed, which may significantly reduce the reflectivity, i.e., the EUV reflectivity of the black border region 24 may be reduced to less than 0.05%. Furthermore, the reflectivity of the non-photochemical reaction zone (150 nm > lambda >300 nm) can be reduced to about 5 to 6%.

In addition to the black border region 24, the morphology of the exposed surface of the substrate 14 may be modified, e.g., roughened or otherwise scattered (as shown at reference numeral 26) to further reduce overlay problems, e.g., over-development of Critical Dimensions (CDs). In particular, the modified surface 26 will reflect or scatter DUV light to prevent it from reaching the next reflector. In this way, the modified topography can be used to prevent radiation overlap and overexposure at the edges and corners of the designed circuit elements.

Fig. 2 a-2 c illustrate different surface morphologies within the black border region according to several aspects of the present disclosure. In several embodiments, the modified surface 26 may be formed by different methods that produce different surface topologies. For example, as represented in FIG. 2a, the modified surface 26' may be a roughened surface that produces random angle scattering. As shown in fig. 2b, the modified surface 26 "may be a sloped surface with a constant angle, e.g., about 20 degrees, resulting in scattering away from the next reflector at a constant angle. Furthermore, as shown in fig. 2c, the modified surface 26 "' may be a sloped surface with a variable angle, e.g., a paraboloid or a concavity, resulting in scattering away from the next reflector at a variable angle. In the embodiment of fig. 2b and 2c, the inclined surface causes the light to be scattered at a predetermined angle.

More particularly, and with reference to FIG. 2a, modified surface 26', i.e., roughened random angle scattering surface, may be formed by additional selective substrate etching to roughen the surface of substrate 14. For example, roughened surface 26' may be formed with a different etching chemistry, such as a fluorine-based chemistry, used to form black border 24. In several embodiments, the fluorine-based etch chemistry may be used with the same mask used to form the black border region 24, thereby reducing overall manufacturing costs. In several embodiments, the roughened surface can be formed by a programmed roughening (surface roughening) of the surface during or after the formation of the black regions. It should be appreciated that the roughened surface 26' produces random light scattering.

In alternative embodiments, the modified surface 26' may represent a different shaped surface that reflects light away from a subsequent reflector, for example. These different shapes may be pyramids, rods, cylinders, etc. In these embodiments, after the black border region 24 is formed and the resist is stripped, a second level of patterning and etching steps may be performed after the black border region is formed. In this process, after the black border region is formed, a resist covering the entire mask may be formed and patterned using a conventional photolithography process to form different shapes. These different shapes may then be transferred to the surface of substrate 14 within black border region 24 using a conventional etching process (e.g., RIE of selective chemistry) to form a surface topography having a particular shape.

Referring to fig. 2b, the modified surface 26 ″ may be an inclined surface formed after the black border region is formed. In fig. 2c, the modified surface 26 "' may be a variable angle surface formed after the black border region is made. In the methods of forming these various modified surfaces, for example, modified surfaces 26 "and 26'", the post-development resist profile (post-developer resist profile) may be altered by exposure to different doses of energy. For example, for the modified surface 26 ", the exposure dose can be varied such that the developed resist profile is thinned from thick (e.g., forming a sloped or angled surface); however, for the modified surface 26' ", the exposure dose can be varied such that the resist profile after development is thinner to thicker (e.g., forming a concave or parabolic surface). Then, an etching process, e.g., RIE, follows to transfer the resist profile to the surface of the exposed surface of the substrate 14 to form the inclined surface 26 "of fig. 2b or the inclined surface 26"' of fig. 2 c.

In an alternative embodiment, sloped profile 26 "may be formed by tilting an inductor in an etch chamber to induce a power gradient profile during black border region etching to intentionally etch the sloped surface, e.g., resulting in sloped etch profile 26" within black border region 24 of fig. 2 b. The same process may be used to form the variable angle profile 26 "' within the black border region 24 of fig. 2 c. Alternatively, the gas flow in the etch chamber may be modulated to establish a gradient density of plasma (plasma) to produce the sloped etch profiles of fig. 2b and 2 c.

The method(s) described above are used in the fabrication of integrated circuit chips. The resulting integrated circuit chips may be sold by the manufacturer in raw wafer form (i.e., a single wafer having a plurality of unpackaged chips), as a bare die (bare die), or in a packaged form. In the latter case, the chip is mounted in a single chip package (e.g., a plastic carrier with leads (leads) affixed to a motherboard or other higher level carrier) or in a multi-chip package (e.g., a ceramic carrier with either or both surface interconnects or embedded interconnects). In either case, the chip is then integrated with other chips, discrete circuit components, and/or other signal processing devices as part of either (a) an intermediate product (e.g., a motherboard), or (b) an end product. The end product may be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor.

The description of the various embodiments of the present disclosure has been presented for purposes of illustration and not limitation, and is intended to be exhaustive or limited to the embodiments disclosed. Those of ordinary skill in the art will appreciate that many modifications and variations are possible without departing from the spirit and scope of the disclosed embodiments. The terminology used herein is chosen to best explain the principles of the embodiments, the practical application or technical improvements over that which is presently available on the market, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. An extreme ultraviolet mask structure, comprising:

a reflective surface comprising a patterned design within an absorbing material;

a black border region at an edge of the patterned design, the black border region comprising a modified surface topography of an underlying substrate to direct light away from a subsequent reflector;

a protective coating of a material having a high atomic number on the reflective surface, wherein the high atomic number is in the range of 40; and

an absorption layer on the protective coating;

wherein a patterned design is formed within the absorber layer up to the protective coating, and the black border region is formed through the reflective surface, the protective coating, and the absorber layer to expose a surface of the substrate.

2. The extreme ultraviolet mask structure of claim 1, wherein the modified surface morphology of the substrate is provided on the underlying substrate with the reflective surface within the black border region.

3. The extreme ultraviolet mask structure as recited in claim 2, wherein the substrate is glass.

4. The extreme ultraviolet mask structure of claim 2, wherein the modified surface morphology is a roughened surface.

5. The extreme ultraviolet mask structure of claim 2, wherein the modified surface morphology is a sloped surface.

6. The extreme ultraviolet mask structure as recited in claim 5, wherein the inclined surface is an angled surface.

7. The extreme ultraviolet mask structure of claim 6, wherein the angled surface is a constant angle surface.

8. The extreme ultraviolet mask structure of claim 5, wherein the inclined surface is a variable angle surface.

9. The euv photomask structure of claim 8, wherein the variable angle surface is a paraboloid or a concavity.

10. The extreme ultraviolet mask structure of claim 2, wherein the modified surface morphology is a shaped surface comprising one of rods, pillars, and pyramids.

11. An extreme ultraviolet mask structure, comprising:

a substrate;

a reflective surface on an opposite surface of the substrate, the reflective surface comprising a plurality of alternating layers of relatively high and low atomic number materials;

a protective coating of a material having a high atomic number on the reflective surface, wherein the high atomic number is in the range of 40;

an absorption layer on the protective coating;

a patterned design formed within the absorber layer up to the protective coating; and

a black border region formed through the reflective surface, the protective coating, and the absorber layer to expose a surface of the substrate, the black border region comprising a modified surface morphology of the substrate.

12. The euv mask structure of claim 11, wherein the modified surface morphology is a roughened surface.

13. The euv photomask structure of claim 11, wherein the modified surface morphology is a sloped surface.

14. The euv photomask structure of claim 13, wherein the inclined surface is a constant angle surface.

15. The euv photomask structure of claim 13, wherein the inclined surface is a variable angle surface.

16. The euv mask structure of claim 11, wherein the modified surface morphology is a shaped surface comprising rods, pillars, or pyramids.

17. A method of fabricating an extreme ultraviolet photomask structure, the method comprising the steps of:

forming a black border region in a mask through a reflective surface, a protective coating of a material having a high atomic number on the reflective surface, and an absorber layer on the protective coating and exposing an underlying substrate, wherein the high atomic number is in the range of 40; and

the surface morphology of the substrate in the black border region is modified to cause deep ultraviolet light to scatter away from reaching the next reflector.

18. The method of claim 17, wherein modifying the surface morphology comprises: after the black border area is formed, the surface of the black border area is roughened by a selective etching process or a program-setting roughening method.

19. The method of claim 17, wherein modifying the surface morphology comprises: changing an energy dose of the resist over the entire black border region to form a gradient resist profile, and etching a sloped resist profile to transfer a slope to a surface of the black border region.

20. The method of claim 17, wherein modifying the surface morphology comprises building one of:

a gradient power distribution across the black border region constructed by intentionally etching sloped surfaces of the black border region by tilting a number of etch chamber inductors; and

a plasma density gradient across the black border region is configured to intentionally etch the sloped surface of the black border region by modifying a gas flow within the etch chamber.